Engines may use a turbocharger to improve engine torque/power output density. In one example, a turbocharger may include a compressor and a turbine connected by a drive shaft, where the turbine is coupled to the exhaust manifold side and the compressor is coupled to the intake manifold side. In this way, the exhaust-driven turbine supplies energy to the compressor to increase the flow of air into the engine.
The compressor is intended to work in an operating range between two conditions, surge and choke. Surge occurs during low air mass flow, when the air flow through the compressor stalls and may reverse. The reversal of air flow may cause the engine to lose power. One source of surge, tip-out surge, may occur when the engine suddenly decelerates. During tip-out surge, the engine and the air flow mass through the compressor may slow down, while the turbocharger continues to spin due to inertia and delays through the exhaust system. The spinning compressor and low air flow rate may cause rapid pressure build-up on the compressor outlet, while the lagging higher exhaust flow rate may cause pressure reduction on the turbine side. When forward flow through the compressor can no longer be sustainable, a momentary flow reversal occurs, and the compressor is in surge.
A second source of surge may be caused in part by high levels of cooled exhaust gas recirculation (EGR). EGR may be used for reducing NOx emissions from diesel engines and for controlling knock in gasoline engines. High levels of EGR may increase compressor pressure while decreasing mass flow through the compressor causing the compressor to operate inefficiently or in the surge region.
Choke occurs when the air flow mass flowing through the compressor cannot be increased for a given speed of the compressor. During choke, the turbocharger cannot provide additional air to the engine, and so the engine power output density cannot be increased.
Therefore, it can be desirable to increase the operating range of the compressor and the turbocharger by reducing the air flow rate before surge occurs and increasing the air flow rate before choke occurs. One solution that has been used to widen the operating point is a passive casing treatment. The passive casing treatment includes a pair of immovable slots that modify the air flow through the compressor. During low air mass flow conditions, the slots of the passive casing treatment may provide a path to recirculate partially pressurized air back to the compressor inlet. The recirculated air flowing through the compressor may enable less air to flow through the compressor before surge occurs. During high air mass flow conditions, the slots of the passive casing treatment may provide a path to short-circuit air flow through the compressor so that the choke occurs at a higher air mass flow rate.
However, the inventors herein have recognized that an effective location for a passive recirculation slot to prevent surge is different from an effective location for a passive recirculation slot to prevent choke.
As such, an example of a turbocharger to address the above issues is described. The turbocharger includes an active casing treatment, an impeller, a casing, and a diffuser. The impeller includes a full blade having a leading edge, a splitter having a leading edge, and an axis of rotation. The casing includes a compressor inlet, an intake passage, a recirculation passage, a recirculation port, a bleed port, and an injection port. The intake passage contains the impeller in a gas flow path downstream from the compressor inlet and upstream from the diffuser. The leading edge of the full blade is upstream of the leading edge of the splitter. The bleed port is downstream of the leading edge of the full blade and upstream of the leading edge of the splitter. The injection port is downstream of the leading edge of the splitter. The recirculation port is downstream of the compressor inlet, upstream of the impeller, and configured to enable gas to flow between the recirculation passage and the intake passage. The active casing treatment is configured to selectively control gas flowing through the bleed port, between the intake passage and the recirculation passage, and selectively control gas flowing through the injection port, between the intake passage and the recirculation passage. In this way, a port may be optimized for both choke and surge conditions and the operating range of the turbocharger may be extended.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.